The present invention relates to a wavelength division multiplex transmission apparatus and, more particularly, to a wavelength division multiplex transmission apparatus capable of compensating for wavelength dispersion on a transmission path.
Generally, in a wavelength division multiplex transmission system, an optical transmission apparatus includes N optical transmitters respectively emitting signal light having wavelengths xcex1 through xcex1 N. After the wavelengths of the signal light have been multiplexed, dispersion compensation units located at the transmission side compensate for the wavelength dispersion on a transmission path. Because the amount of dispersion compensation necessary for implementing required transmission quality differs from one wavelength to another wavelength, N different dispersion compensation units are necessary for a wavelength division multiplex transmission system handling N different waves to execute optimal dispersion compensation.
The above transmission system includes N optical transmitters each using a 1.55 micron band semiconductor laser as a light source, a coupler for combining light output from the transmitters, N dispersion compensation units serially connected to the coupler, and another coupler for combining light output from the dispersion compensation units. Each dispersion compensation unit includes a dispersion compensating section, an optical direct amplifier, and a splitter for separating only light having a particular wavelength xcexx (x=1xe2x88x92N). With these structural elements, each dispersion compensation unit executes optimal dispersion compensation with one of the input combined light having a particular wavelength and separates and outputs the light having the particular wavelength.
It is a common practice with the above system to connect the optical transmitters, dispersion compensation units and so forth by connector connection using an optical patch code. Each dispersion compensation unit therefore includes a monitor circuit for monitoring the level of the 1.55 micron band signal light and thereby detecting an error degrading transmission quality, e.g., defective connector connection or the shutoff of the patch code.
However, the problem with the transmission apparatus of the kind described is that the level of the signal light differs from one connecting section to another connecting section in a complicated manner due to, e.g., optical pre-emphasis which sets particular signal light level for each wavelength and outputs such wavelengths to a transmission path. It is therefore extremely difficult to set a single threshold level in order to monitor errors in the level of signal light ascribable to, e.g., defective connection between the units or the shutoff of the patch code.
It is therefore an object of the present invention to provide a simple, low cost wavelength division multiplex transmission apparatus capable of detecting an error occurred at any connecting section easily and reliably.
In accordance with the present invention, a wavelength division multiplex optical transmission apparatus for transmitting a plurality of signal light of different wavelengths by multiplexing the wavelengths includes a plurality of optical transmitters each for outputting signal light having a particular wavelength. A first coupler combines signal light output from the plurality of optical transmitters. A plurality of dispersion compensation units respectively execute dispersion compensation with the signal light combined by the first coupler and separate the respective compensated signal light. A light source outputs light having a preselected wavelength to be input to the plurality of dispersion compensation units. A plurality of photo-detectors each detects the level of the light having the preselected wavelength. A second coupler combines signal light respectively separated by the plurality of dispersion compensation units.